This invention relates generally to rotating mechanical elements such as rotor disks, and more specifically to balancing of rotors in turbomachinery.
A gas turbine engine includes a turbomachinery core having a high pressure compressor, combustor, and high pressure turbine in serial flow relationship. The core is operable in a known manner to generate a primary flow of propulsive gas. A typical turbofan engine adds a low pressure turbine driven by the core exhaust gases which in turn drives a fan rotor through a shaft to generate a bypass flow of propulsive gas. In the case of a high bypass engine this provides the majority of the total engine thrust.
The fan rotor includes an array of fan blades extending radially outward from a fan disk. During operation of the engine, it is important that the rotor be statically and dynamically balanced. Any substantial rotary unbalance within the fan rotor can cause undesirable mechanical loads in the fan rotor as well as connected components such as bearings, bearing supports, and fan support frames. This excessive loading can lead to shortened life and/or component failure.
A rotor may be balanced by assembling the blades in the rotor so that their mass is distributed as evenly about the circumference as possible. The rotor may be further balanced by installing one or more trim weights in selected locations. For example, if a specific blade is heavier, then one or more trim weights would be installed in the rotor at a location opposite to the heavy blade.
A desire exists to increase fan bypass ratios. As bypass ratios increase, the fan diameter increases and/or the hub flowpath diameter decreases. One problem relating to such fan rotor configurations is that existing fan balance weight configurations may not be capable of removing all unbalance caused by a heavy blade.